The TEL Scare That Wasn't

Although I can't be certain, it appears that most AVweb readers were spared last week's pointless #^%$storm du jour, but it contained something interesting, so I'm compelled to mention it here. Specifically, our news inboxes took in some stories from the UK and a chemical specialty magazine that said Innospec, supplier of tetraethyl lead, the critical octane booster in avgas, would end TEL production by the end of this year.

This was reported in several UK newspapers that took up the case against TEL after a
provocative article in Mother Jones magazine claimed, among other things, that crime rates were directly related to airborne lead emissions from gasoline. The magazine claimed that lead emissions may explain up to 90 percent of the rise and fall of violent crime during the past half century. Tall claims, no?

If the TEL extinction part were true, we would be in big trouble in GA. The wheels of the FAA are slowly grinding to find an unleaded replacement for 100LL, but it will be at least three years, if not five. If TEL really dried up, so would avgas. But it isn't and it won't, unless the refiners decide they don't want to make 100LL anymore. We contacted Innospec who told us that it is indeed phasing out production of TEL for automotive fuels as the three countries that still use it—Iraq, Algeria and Yemen—transition to unleaded fuels.

On the subject of aviation, Innospec's Alistair Thompson said the company is unambiguous: "Innospec has a scalable manufacturing operation in place to be able meet the demands of the GA industry for TEL-B. We reiterate that we have no current plans to cease the manufacture or supply of TEL-B and, whilst there is continued demand for 100LL, we will continue to support the industry during the phase out of the product."

Key word above: phase out. Don't get the impression that anyone thinks leaded fuel is anything but a legacy. The decision to eliminate it has been made and it won't be reversed, so don't bother to chop the dead horse into small cubes and insert it into the word blender for further reduction. We've settled the argument. Now it's only a matter of keeping the lifeboat afloat long enough to bridge into the unleaded future.

It's always possible that Innospec's plant could blow up and that its stockpiles of TEL could be lost or that environmental interests in the UK could force the issue. Or maybe those rumors we keep hearing that Shell and Chevron desperately want out of the avgas business will come true at last, even as their tankers keep arriving at airports with fresh loads of 100LL. It's also possible that Easter Bunny will be the next president of AOPA. But alas, we're dealing with probabilities here and there's a high probability TEL will be available for as long as it's needed.

And by the way, it's not true that Innospec is the only source of TEL. I had heard from Chinese sources at Oshkosh that China makes its own avgas indigenously with its own TEL production. Lycoming's Michael Kraft, who has traveled extensively on aviation business in China, confirmed this. Whether China could export TEL elsewhere is an unknown, but it's clear that they make it.

Back to the Mother Jones piece. I don't know whether to be alarmed, appalled or amused by the findings in this article. The graphs of crime rates overlaid with lead emissions seem a little too perfect to believe. What if we plotted other variables, like the production of mushrooms or pork belly futures? The consumption of light beer? Or beets? Would there be similar correlations with the crime rate? Was the science controlled for other factors? The article is a little vague on this. I find it unconvincing, but you can judge it for yourself. Thankfully, it doesn't mention the microscopic amount of lead emissions general aviation is still responsible for. We're such a minor industry as to be off the radar. For once, maybe that's a good thing.

While on the subject of unleaded fuel, Todd Petersen, who developed hundreds of mogas STCs during the 1980s, complained that my story last week updating various fuel projects incorrectly said mogas wasn't an approved aviation fuel. Fair point. I should have said it's not a purpose-made aviation fuel, but the STCs mean it is aviation approved for many engines.

Comments (60)

Well the lack of comments here suggest perhaps this topic is of little intrest to the AVweb loyal or its a topic that has been over-blogged about. Nonetheless, I know there are a lot of people who join Todd Petersen in believing mogas should be a candidate for fixing this problem. I'm no expert but I'm quite sure its well documented where high octane mogas could be used in most all of our engines. Most with no modifications and some with system upgrades such as new pumps or power/CHT temperature limitations, or by water injection. I understand about mogas shelf life and the lack of non-ethanol supply, but those seem like easier fixes than waiting 5 years of shaking out a drop-in fuel that is likely going to be more expensive than 100LL. If AOPA, EAA, AVweb, etc. would somehow get together on this, with the help from powersport and boating communities, and perhaps even environmental groups who want to elimnate the lead, then maybe congress would remove the Ethanol mandate from high octane mogas. This alone would allow STC'ers like Petersen, the EAA, or even some new startup to start testing airframes with fuel refined in 2013 which we all know is more consistent than it has ever been. Please someone with a little clout step up and get the ball rolling!

When the UK manufacturer stops producing for the three remaining countries still burning leaded gas hold on to your wallets. The price should go up substantially for this product and we will feel it at the FBO.

The U.S. Government is not trying to get us cheaper gas or more available gas (just like they are not trying to get us cheap space travel). The U.S. Government obviously does not care to help us out or even get out of the way when it comes to GA.

That means that we can't predict what will happen; The FAA is asleep and our future hangs on whatever random crisis comes along.

Wow! You had my full and undivided attention when you put the Easter Bunny as the hopeful next President of AOPA into reach. My nomination would have been Homer Simpson, but for lack of better choices, I will do my American GA Pilots duty and bow just as deeply to the Easter Bunny. Homer could take over LaHoods job, no? Meanwhile we can all leisurely travel to China in our jets and rich man aeroplanes (lets skip the fish for fear of fainting) and learn a thing or two about general aviation growth and sustainability.

Michael, everyone is out looting and frauding. Or something else criminal.

I haven't previously seen the stuff Mother Jones is reporting but the lead-crime thing isn't new. I've only seen correlational evidence so far. Since correlation isn't causality, the last I heard is "more research needed." Maybe there's something in it. Some interesting research has recently linked inhaling burnt hydrocarbons with the rise in Autism. Kids who grow up near major roads are at a greater risk. Again, it's correlation only - might be the sound of car horns for all we know.

Ohh and for the Mother Jones report...shouldn't all us pilots be walking dead with lead poisoning? As a full time instructor I sit no further than a couple of feet from the exhaust stack of these poisoning machines. Granted the majority of the time i'm traveling with the exhaust exiting safely behind me, but during pre-flight I regularly get sumped fuel on my hands and I'm pretty sure I breath some exhaust during startup, taxi, and run-up. Has anyone tested us pilots for lead levels? If this article has merit, then that my explain why I'm loosing my memory! :)

Note that, according to retired Shell Aviation fuel and lubricant expert Ben Visser, Shell actually stopped producing 100LL avgas over two decades ago. See his comments on his blog at GAN, "Visser's Voice" from October 14th, 2012 "Why does 100LL cost so much". What we buy as Shell Avgas in the Southeast actually comes from a major unbranded fuel producer in the upper Midwest. From my discussion at AirVenture 2012 with the head of aviation fuels for this company, the only reason they themselves continue producing avgas is as a courtesy to their Jet-A customers, where the real money in aviation fuel is made.

If TEL were actually the cause of crime, it seems like crime would be down to almost nothing since there is no longer any TEL in autogas. The only crime should be around GA airports. Well, the price of avgas is a crime.

Mogas is not only aviation approved by the STC process but is also widely approved by the LSA ASTM process for 99% of LSA aircraft and is being approved by both Lycoming and Continental for certain new engines, like to Continental O-200-AF.

So far all of this discussion of TEL completely ignores what is probably the most important point, the business model for TEL is doomed, both from the production standpoint, Innospec, and the customer standpoint, the producers of 100 LL Avgas. If one were to dig down into the announcements by Innospec they would find that TEL production at their single plant has gone from 24/7 production down to a single shift 5 days a week. What will it be when aviation TEL is the last TEL product, 1 day a week, one day a month? It will be miniscule and why does anyone believe that the Innospec bean counters won't decide to cancel it? Because of the constantly declining demand for 100 LL avgas worldwide, Innospec faces declining production of aviation TEL each year. The avgas producers are looking at a constantly declining demand each year and even the prospect that the replacement for avgas might not even be a product they would make. When are their bean counters going to throw in the towel? The avgas production in this country is totally opaque. We have no idea who makes it or where it is made and we have no idea when the bean counters are going to pull the plug.

Cont'd
My guess is it will be long before an unleaded 100 octane replacement is found, even if it only 5 years away. Pretty ironic that we have been searching for a 100 octane unleaded avgas for about three decades and maybe we're five years away, and cellulosic ethanol producers have been five years away from a commercially viable cellulosic ethanol production process for the last thirty years too. The further irony is that because of the total lack of support for mogas infrastructure on our airports by the FAA and aviation alphabets, the federal RFS mandate will probably seal the demise of ethanol free mogas by the end of this year. Ethanol quotas demanded by EISA 2007 were just published last Friday, three months late, they indicate that more ethanol must be blended into our auto fuel supply than can be absorbed by taking every drop of auto gasoline E10. It has only been a loophole in the law that allows producers to fudge forward 20% of their quotas to the next year that kept us from hitting the blending wall in 2012.
The perfect storm is brewing. There is a good chance that by 2014, Innospec may have thrown in the towel with TEL, the gasoline producers may have finally figured out that there is no future in making 100 LL, between the environmental pressures and the ridiculous business model and there may not be any source of ethanol free auto gasoline in the U.S., especially premium unleaded as refiners convert to making sub-octane BOB for more efficient E10 production.

Dean, they use the word "scalability" in their announcement and I guess I'm more willing to take them at their word than you. Production managers like 3 shifts running but that's not always necessary for profitability. The technology is old, the equipment paid off and there is a guaranteed, if slowly shrinking market. They've also got an effective monopoly so their only real concern is to maximise profit while not making competition viable. This isn't like Kodak shutting down 35mm film production. They've got a classic captive market and I'm betting they can make a profit until well after a new additive comes out and is mandated.

I think free market forces may help keep TEL in production, even if Innospec walks away from the business. If Innospec loses commercial interest in producing TEL, they'll simply start adding zeros to the price tag to make it interesting again. Others will notice, and take an interest in producing TEL themselves.

China has been happy to supply lead-laden products to the US in the past, so they will likely be a willing candidate in the future.

I am fortunate to be based at FYV where we have 91 oct ethanol free no lead available. Since I have an experimental I dont have to comply with the ridiculous STC for it. I have to have a tank of 100ll for summer tho as I have a vaporlock problem in hot weather after sitting with hot engine.

The reply to Michael Plervy's question is that he might be OK, but his children/grandchildren might not be -- especially if he does not change his clothes before going home.
Googling Lead Levels in Mechanics' Children bought up this WHO report at the top of the list who.int/bulletin/volumes/85/9/06-036137/en/index.html.
I also remember reporting, long ago before this internet thingy was around and when some were saying removing lead from petrol was silly, on research in the UK about levels of lead on mechanics' overalls.
Once again, no particular problem if you brain has stopped growing, but -20 IQ points for youngsters.
Similar research was done on asbestos on mechanics' overalls before they stopped using asbestos in brake pads, and some were saturated with it.
It helped one or two mechanic's wives who developed the particular cancer associated with asbestos exposure, get compensation / pensions.

I am fortunate to be based at FYV where we have 91 oct ethanol free no lead available. Since I have an experimental I dont have to comply with the ridiculous STC for it. I have to have a tank of 100ll for summer tho as I have a vaporlock problem in hot weather after sitting with hot engine.

For those in the US unaware of what is going on in the EU take a look from the minutes of a meeting held at the UK Civil Aviation Authority. While the US is still wondering what to do - in the EU the unleaded AVGAS is already a reality.
A second meeting of the European unleaded AVGAS group was recently held at Gatwik in the UK.
There are more details and lots of presentations on hjelmco.com/news.asp?r_id=91973

For those in the US unaware of what is going on in the EU take a look from the minutes of a meeting held at the UK Civil Aviation Authority. While the US is still wondering what to do - in the EU the unleaded AVGAS is already a reality.
A second meeting of the European unleaded AVGAS group was recently held at Gatwik in the UK.
There are more details and lots of presentations on hjelmco.com/news.asp?r_id=91973

So long as Innospec (or someone else) can make more profit supplying TEL than if they used the same facilities to produce something else, they will continue to sell TEL -- even if it's only a fraction of what they used to sell.

The amount of lead in 100LL is far below the amount that was in 80% of ALL gasoline burned between 1930 and 1970.

I was born in 1957, and spent most of my growing years in the Los Angeles Basin. Not only was there routine smog (from leaded gas), my neighborhood also was home to several dragster and hot rod builders, boat owners, dozens of lawnmowers, go-karts, mini bikes, and pretty much anything else that had a gas engine.

Then there was all the time that I spent around airplane engines, starting when I was 7 years old.

The last time I bothered to take the battery of tests, my IQ was rated at 158 points.

Are you telling me that if I had lived on an Amish farm, away from all of those leaded gas fumes, my IQ would be 178?

Keith, it would probably be beyond 300 and you wouldn't sink in the bathtub! 20 years ago I sat with a Cessna Rep in Europe who told me to bugger off about non lead, efficient engines in Cessna's rivet holders. He stated: "Where I fly, AVgas is a dollar a gallon and we have more unregistered airplanes flying in AK than you guys have in all of Europe!" I wish I could speak with this clown today...

That guy is probably using autogas anyhow -- I don't think they have to add alcohol in Alaska, and they sure don't have much of a vapor lock problem!

Can you imagine the scene in 20 more years, when the cops bust down a door and drag out guys who were running an illicit ethyl lab . . ? Or having guys standing on street corners in industrial parks, passing small bags full of gray powder to pilots who stop their cars and hand them money . . ?

If there's money to be made, someone will produce it. The question is will any of us be able to afford it by the time it gets to the pump? Those rotax engines that so many look down on may require a second look. That of course means looking at different airframes. I wish my FBO would provide ethanol free mogas but wishing won't fuel my Continental.

Mogas will start to appear as the LSAs and 4-seaters appear with the new Continentals and Rotax that burn E10. The new carbon wonders are filled with the leading edge in avionics, CAD designs, hyper efficiency, and safety. The old tin clunkers are equivalent to trying to find a 57 Buick with a cast iron block burning leaded gas. AM radio in all.

Don,t be so pessimistic.
Read my presentation I had for the California GA-community where I presented solutions that will fit for almost everyone. You shall not need to convert to
LSA or ultralights. Technology will help us to live without lead.
hjelmco.com/news.asp?r_id=83471

It would be nice to see ethanol free mogas in the highest available octane at most all airports. And some FBOs who have leaded gas for the relatively few who absolutely have to have it. Sort of like the old days but reversed when all FBOs had avgas and a few also sold mogas. The cost of the STC seems really low compared to the price delta with avgas vs mogas.

It would be nice to see ethanol free mogas in the highest available octane at most all airports. And some FBOs who have leaded gas for the relatively few who absolutely have to have it. Sort of like the old days but reversed when all FBOs had avgas and a few also sold mogas. The cost of the STC seems really low compared to the price delta with avgas vs mogas.

I love good humor, but the unleaded-gasoline story is an existential issue for GA. No fuel = no flight. This industry has three options:
1. Keep making leaded avgas.
2. Come up with a fungible drop-in replacement for leaded avgas.
3. Re-engine the fleet, so it can burn whatever fuel is available (likely kerosene).

The EPA is likely to take choice # 1 off of the table. Economics - not science - will determine which of the remaining two choices will prevail. This entire industry will be re-shaped by that decision.

I believe it is a given that at some point, leaded avgas will be a thing of the past. For the higher-power avgas-burning engines, I don't think there will be a true 1-to-1 drop-in replacement. Most of the experimental drop-ins weigh more per gallon than 100LL, which means a full-tank top-off will provide less payload, and for some that won't be an acceptable trade-off. That leaves either engine modifications (which may or may not impose equally-unacceptable operating limitations), or re-engining (to run at equal power outputs, but on unleaded avgas or Jet-A).

The lower-powered engines should run fine on 94 or 96UL with an STC, so the lower end of the spectrum will likely be fine with whatever solution eventually comes about. It's the higher end that the future looks more questionable for (many of which are not these so-called "tin lizzies").

Lars:
I read your California presentation; very good. I think you have a real solution that is viable. What we need over here is a clear deadline so that fuel retailers do not have to guess at what is going to happen. Perhaps a date that coincides with our ADS-B mandate of January 1, 2020 or something like that.

Stephen -- glad you found it -- the solutions are there.
Without saying too much, think on the new Lycoming IO390 engine now with 210 hp which will go into Pipistrel Panthera aircraft. Look at the old Lycoming IO 360 with 200 hp. Basically same engine size , moounting etc. The difference is only that the IO390 will run on AVGAS 91/96 UL. Then think that todays Lycoming IO 540 with 300 HP is an IO360 but with 2 additional cylinders (260+180=540). Today Lycoming has a TIO 580 engine out there. Well these 210 HP could easily be 305 HP and also
operate on unleaded AVGAS 91/96 UL. Then add the turbocharger which actually decreases octane need (compression ratio is lower in turbocharged engines) and then you are there.
Technology solves our problems.
Then we have Todd Petersens waterinjection systems giving us a boast on more than 12 MON. Add that to AVGAS 91/96 UL and you are at 103 MON. Instead of crying for lead -- assist/help/promote the companies that will solve the lead problems.

Paul, I think you're a bit unfair to Mother Jones. As you mention, the article did not cite avgas as a significant source of lead poisoning. It focused on lead at ground level -- in the dirt, in paint, etc. More importantly, the article did acknowledge the very natural skepticism that lead and crime could be so linked.
The author advanced a hypothesis worth thinking about: that lead poisoning screws people up, and that screwed up people are more likely to be criminals. And then the author proceeded to show why statistics link the two FAR more than one sees in the average slapdash public health research paper. I see a LOT of correlation-versus-causality confusion in my own work, and so I was on the lookout for this. But I urge people to read the actual article, study the graphs, and see for themselves. The neighborhood-by-neighborhood charting of crime rate versus ground-level lead makes it difficult to dismiss the author's premise out of hand.
I didn't see the article as smugly saying "proof beyond all doubt." I saw it as saying, "These correlations are so intricate, they are hard to dismiss out of hand."
The amount of lead considered to be toxic gets lowered every time scientists visit the issue. It's nasty stuff.
I've spent enough time with children who've undergone lead poisoning, and seen their lack of impulse control, that I don't ridicule the author's premise.
Full disclosure: the founder of the Lead Safe America Foundation is a friend of mine.

The aging fleet of leaded GA planes out there can be phased out if mfr are FORCED to put in engines that burn E10 and E20 now. That is the next step. For now, the planes burning E10 mogas like the LSAs using a Rotax are way ahead of he game. And the bonus is they are FAR more fuel efficient. As fuel costs rise, less GA guys with old 100LL planes will even be able to AFFORD to fly. maybe that is another way to drive them out of their antiques.

Maybe so, John. But here's the headline and deck on the article: "America's Real Criminal Element: Lead
New research finds Pb is the hidden villain behind violent crime, lower IQs, and even the ADHD epidemic. And fixing the problem is a lot cheaper than doing nothing."

I find that quite categorical for an article that might otherwise be describing a theory supported by compelling if not definitive data. At the end of the article, the author, after admitting meaningful economic data is all but impossible to acquire, then proposes that a lead remediation program of $20B a year would payback at least $200B a year in higher cognitive function, higher IQ and reduced health issues.

C Bigs, I will be driven out of antiques when they pry the stick out of my cold dead hand. You talk like ethanol is a good idea. People are starving all over the world and you want to pour corn in your fuel tank. Ethanol is a lower BTU fuel than gasoline and absorbs water. Its energy output is woefully short of the energy input to make it. The only reason we're putting it in gas tanks is congress has mandated that we taxpayers will subsidize this economically unviable waste of what should be going into food and good whiskey.

Richard Montague, thank you for clear thinking. Ethanol is a really stupid political ploy, and someday it will be remembered in the public policy hall of shame, along with high-rise public housing projects and Soviet five-year plans.
Someday, we had better learn to grow good fuels -- for transportation, for electricity production, for home heating, and so on -- but I don't think corn will ever be the plant of choice. If we could get over our prissy attitude towards hemp, I think there's a lot of promise there.

John, it's got to be on land that is no good for anything else. Even hemp, with its superior properties, is cutting it too close. My pick is algae grown in big bags at sea or on useless desert sites ... there's a can of worms. :-)

Ethanol is not a good idea, but it IS reality. You still running your lawnmower or car on leaded gas? no. It is obvious where all this is going. And your cold dead hands are a laugh. If you still want to fly in five years you better find a way to dump your dinosaur and get a non-leaded engine.

Running my car and lawnmower on leaded? Nope, but not running on ethanol contaminated fuel either, just plain pure unleaded. By the way, a Warner Super Scarab engine will run just fine on unleaded without
ethanol and so does the Harley.

Richard. No such thing as PURE unleaded. All unleaded gas in the USA is E10. 10% ethanol unless you are able to get special blends, this is what you are running in your lawnmower and car. By the way, watch for the EPA to push out E20 soon. This will really mess with your Harley.

Sorry, I gotta call BS on that. E0 is available for anyone wishing to go a little out of their way. There are hundreds of cars running on it around here, available from a local distributor at about a $.30 premium over the E10 which, I agree, is now the standard. I will be happy to give you the distributor's phone number who will sell you a truckload of EO or direct you to the local gas stations who will sell you a couple of liters to fill your Vespa.

As to the immorality of leaded fuels, it is probably not much greater than putting food in your fuel tank while much of the world is starving.

I'm having trouble following some of this discussion. Please enlighten me:
E10 = 10 percent ethanol, correct?
E20 = 20 percent ethanol, also correct?
E20 will have twice the problems of E10 -- lower energy density, lower fuel mileage, more water in the fuel, more corrosive to gaskets and other fuel system parts -- correct?
But why is E0 (presumably 0% alcohol) part of a discussion of lead? Are you guys mixing up lead content and alcohol content? We had unleaded gas for years before the politicians started squirting corn into gasoline.

"But why is E0 (presumably 0% alcohol) part of a discussion of lead? "

Because mogas is suitable for at least 80 percent of aircraft engines in the fleet, but the STCs require non-ethanol gasoline. It's not just older engines. Some new ones, too are type certified for mogas. I don't remember if the requirement for E0 relates to fuel system components or corrosion or both. Perhaps Todd Petersen can educate us.

MTBE is not blanket banned by the EPA, but some states have restrictions on it, which stemmed from ground water contamination issues from leaking tanks when MTBE was the oxygenate of choice. It is still used in Europe and Japan.

Paul -- I doubt - correct me if I am wrong - "MOGAS in the US is suitable for 80 %" of the fleet. When MTBE was removed you lost octane and you put ethanol instead to raise octane again. Gasoline without ethanol or MTBE has low octane unless something elses increases the octane. I would say MOGAS could be octane wise suitable for AVGAS 80 engines if you can handle all other issues such as vapor pressure.
MTBE is not the choice of oxygenate in Japan - but ETBE is.

Paul -- I doubt - correct me if I am wrong - "MOGAS in the US is suitable for 80 %" of the fleet. When MTBE was removed you lost octane and you put ethanol instead to raise octane again. Gasoline without ethanol or MTBE has low octane unless something elses increases the octane. I would say MOGAS could be octane wise suitable for AVGAS 80 engines if you can handle all other issues such as vapor pressure.
MTBE is not the choice of oxygenate in Japan - but ETBE is.

Paul - I have read what they are saying. For our population in Sweden we had unleaded grade 80 AVGAS with MON 82+ during the 1980:ies. For that population we covered about 50 % of the fleet. For this reason unleaded grade 91/96 was developed 1990 -- and that fuel covered about 70 % of the population. Now with so many Rotax engines out there the grade 91/96 unleaded is good for 90+ %. The grade 91/96 UL has a mon of 93+.
Does it in the US exist any MOGAS without ethanol which has a high octane i.e. more than 87 in MON+RON/2?

An 87 AKI would mean around 83 MON - that is an AVGAS 80 with a small marginal. Long time ago MOGAS had lead to get the high AKI 91. If you want to go there today without lead, ethanol, MTBE etc -- the choice would be to add alkylate or aromatics -- ´but then you are back on a special fuel like AVGAS. Alkylate is used in AVGAS to increase octane numbers. If you want to go unleaded and with no ethanol no ETBE no MTBE you would need an octane boster.
EASA in Europe has made a fleet survey and octane requirements on engines as per type-certificate which you can
find on hjelmco.com/upl/files/77810.pdf

The Rotax is certified to run on 91 octane with or without E10. The new continental dual is also certified to run on 91 octane mogas and diesel. The CTLSi will run on 91 octane with E10 or 100LL. BUT the lead makes a mess in the oil and should be zapped by using Decalin.

It is easy to misunderstand as there are several octane numbers. What you find on the pump in the US is called
AKI which is Motoroctane (MON) + Researchoctane (RON) divided by 2.
Then in the EU we only work with RON.
In AVGAS we use Aviation rating which his close to MON.
So super MOGAS in the EU is RON 98 which is about 86 MON or aviation rating.
So when you look at Lycoming SI 1070 and octane rated engines, original AVGAS 91 engines actually certified to burn 91 Aviation Rating (MON) , there is no standard MOGAS in the world that reaches 91 MON. Some AVGAS 91 engines have later been found to operate on lower octane because there was no AVGAS between AVGAS 80 and AVGAS 91. To be on the safe side always look into what the engine manufacturer states as minimum octane, and into the airframe producers manual (Owners Handbook) for maximum cylinder head temperatures and other engine parameters that should correspond to data from the engine manufacturer. A neat installation of an engine in an airframe could result in other octane requirements than the engine manufacturer originally has specified.